The present invention relates to a seat belt tensioning device for a vehicle, etc. to protect a passenger or occupant at an urgent time such as upon an impact of the vehicle by restraining him by a tensioned seat belt.
Conventionally, a seat belt tensioning device of this general type is provided with a piston rod of which one end is connected to the seat belt, a piston which is connected to the piston rod, a cylinder for receiving the piston slidably therein and a driving means which operates the piston to slide relative to the cylinder at an urgent time. By means of the driving means, the piston is slid or moved within the cylinder to tension the seat belt.
However, in the conventional tensioning device having such a construction as described above, the cylinder is required to have enough length to obtain a piston stroke equal to the tensioning quantity or length desired for the seat belt. Furthermore, it is required to project the piston rod outside of the cylinder by a length equal to the piston stroke. Therefore, a space of at least two times as long as the tensioning length of the seat belt is necessary. Further, the space must be secured along one straight line. As a result, the conventional device cannot be easily installed in a limited space within a vehicle body.
From the above described circumstances, the present inventors have proposed a seat belt tensioning device in which a bellows shaped flexible body is employed in place of the conventional cylinder (U.S. patent application Ser. No. 20,045).
In the above described seat belt tensioning device, one end of the bellows shaped flexible body is connected to a fixed member while the other end thereof is connected to a movable member. And in the sealed chamber formed by the bellows shaped flexible body, the fixed body and the movable member, a seat belt or a rod member which is connected to the seat belt is inserted and connected to the movable member therein.
At an urgent time such as upon an impact of the vehicle, high pressure gas is supplied to the sealed chamber to elongate the flexible body. The movable member connected to the flexible body is moved together with the flexible member to tension the seat belt. Consequently, the occupant is restrained on his seat by the tensioned seat belt.
The present invention provides a seat belt tensioning device by which the device proposed by the inventors is improved furthermore.
Accordingly, one object of the present invention is to provide an improved seat belt tensioning device provided with a flexible member.
Another object of the present invention is to provide a seat belt tensioning device provided with means for elongating the flexible member into a predetermined direction and certainly operating to tension the seat belt.
Still another object of the present invention is to provide a seat belt tensioning device provided with means for limiting the tensioning force of the seat belt into a predetermined value and means for preventing the seat belt from returning, having excellent safety.
Further object of the present invention is to provide a small sized seat belt tensioning device in which the extending direction of the seat belt and the elongating direction of the flexible member can be freely selected as desired.